High School Biology : Cell Functions

Study concepts, example questions & explanations for High School Biology

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Example Questions

Example Question #1 : Understanding Receptors And Ligands

Which of the following is NOT true regarding receptors and ligands?

Possible Answers:

Ligands usually make covalent bonds with their receptors.

It is possible for a receptor to bind more than one ligand.

Ligands are usually proteins.

The receptor for a ligand may either be on the cell's surface or inside the cytoplasm.

Binding of a ligand always turns on the protein to which it is bound.

Correct answer:

Ligands usually make covalent bonds with their receptors.

Explanation:

Ligands and receptors are both usually proteins. Since proteins can fold into a wide variety of shapes, the receptor-ligand interaction is very specific. In some cases, certain receptors will bind two ligands that are similar in structure. For example, hemoglobin binds to both  and , but binds  with much higher affinity. Ligands bind receptors using only weak bonds (hydrogen bonds and Van der Waals forces). Depending on the nature of the ligand (whether it can cross the lipid bilayer or not), its receptor may be either on the cell's surface, floating in the cytoplasm, or on the nuclear membrane.

Example Question #1 : Understanding Receptors And Ligands

Which of the following includes the four most common groups of ligands in biology?

Possible Answers:

Substrates, inhibitors, activators, and tracers

Inhibitors, activators, neurotransmitters, and tracers

Substrates, activators, neurotransmitters, and tracers

Substrates, inhibitors, neurotransmitters, and tracers

Substrates, inhibitors, activators, and neurotransmitters

Correct answer:

Substrates, inhibitors, activators, and neurotransmitters

Explanation:

In biochemistry, ligands are any substance that forms a complex with a biomolecule to serve a biological purpose. The four primary types of ligands have their functional state determined by their three-dimensional chemical conformation. Tracers in the body often take the form of radioligands, but are not ligands themselves.

Example Question #1 : Transport And Signaling

Chemotaxis refers to movement of an organism in response to which of the following stimuli?

Possible Answers:

Chemicals

Gravity

Vibrations

Sound

Light

Correct answer:

Chemicals

Explanation:

Chemotaxis refers to the movement of an organism in response to a chemical stimulus. Single or multicellular organisms may direct their movements according to certain chemicals in their environment. This is important because these organisms need to find food, flee from harmful substances, and chemotaxis also aids in development. Positive chemotaxis is movement towards a higher concentration of the chemical, whereas negative chemotaxis is movement away from the chemical.  

Example Question #1 : Understanding Cytoplasmic Proteins

In which cellular compartment does glycolysis take place?

Possible Answers:

Inner mitochondrial membrane

Golgi apparatus

Intermembrane space

Cytoplasm (Cytosol)

Mitochondrial matrix

Correct answer:

Cytoplasm (Cytosol)

Explanation:

Glycolysis (the process of breaking down glucose) takes place in the cytoplasm, or cytosol—the aqueous portion of the cytoplasm. It is in the cytoplasm where the enzymes required for glycolysis are found.

The citric acid cycle takes place in the mitochondrial matrix, and the electron transport chain takes place along the inner mitochondrial membrane in order to pump protons into the intermembrane space.

Example Question #2 : Understanding Cytoplasmic Proteins

What is the function of a kinase?

Possible Answers:

Remove phosphates from ligands

Add ubiquitin to the ligand

Add phosphates to ligands

Change the structure of the ligand

Correct answer:

Add phosphates to ligands

Explanation:

The addition and removal of phosphate groups can serve critical functions in the regulation of protein activity. The binding or uncoupling of phosphate groups frequently serves to activate or deactivate proteins.

A kinase is an enzyme that phosphorylates—or adds a phosphate group to—its ligand.

A phosphatase removes a phosphate group from its ligand.

Several different types of proteins can change the structure of a ligand, such as isomerases, and ubiquitin ligases add ubiquitin to their ligands.

Example Question #3 : Understanding Cytoplasmic Proteins

What is the function of a phosphatase?

Possible Answers:

Add a phosphate to its ligand

Remove a phosphate from its ligand

Add an ubiquitin to its ligand

Change the structure of its ligand

Correct answer:

Remove a phosphate from its ligand

Explanation:

The addition and removal of phosphate groups can serve critical functions in the regulation of protein activity. The binding or uncoupling of phosphate groups frequently serves to activate or deactivate proteins.

A phosphatase removes a phosphate group from its ligand.

A kinase is an enzyme that phosphorylates—or adds a phosphate group to—its ligand.

Several different types of proteins can change the structure of a ligand, such as isomerases, and ubiquitin ligases add ubiquitin to their ligands.

Example Question #141 : Cell Biology

What is the function of an ubiquitin ligase?

Possible Answers:

Remove a phosphate from its ligand

Add an ubiquitin to its ligand

Add a phosphate to its ligand

Remove an ubiquitin from its ligand

Correct answer:

Add an ubiquitin to its ligand

Explanation:

Ubiquitin ligases add ubiquitin to their ligands. The addition of ubiquitin acts as a signal that a protein has become ineffective and is ready for degradation. When multiple ubiquitin residues have been added to a protein molecule, it is transported to the lysosome in the cell to be digested.

A phosphatase removes a phosphate group from its ligand.

A kinase is an enzyme that phosphorylates—or adds a phosphate group to—its ligand.

The addition and removal of phosphate groups can serve critical functions in the regulation of protein activity. The binding or uncoupling of phosphate groups frequently serves to activate or deactivate proteins.

Several different types of proteins can change the structure of a ligand, such as isomerases.

Example Question #41 : Cell Functions

In regard to cellular membranes, what does it mean to be selectively permeable?

Possible Answers:

Molecules and ions can pass freely through the phospholipid bilayer

Polarization of the cell membrane allows for no entrance of foreign molecules or ions

Polarization of the cell membrane allows for passive transport of all foreign molecules or ions

Molecules and ions are always kept to the exterior of the phospholipid bilayer

Molecules and ions outside the cell are selected to enter the cell via active or passive transport through the phospholipid bilayer

Correct answer:

Molecules and ions outside the cell are selected to enter the cell via active or passive transport through the phospholipid bilayer

Explanation:

A cell must exchange molecules and ions with its surroundings.  This process is controlled by the selective permeability of the plasma membrane.  Passive transport requires no energy from the cell; molecules like water can diffuse into and out of the cell through the phospholipid bilayer freely by way of osmosis.  Other molecules and ions, like sodium, are actively transported across the phospholipid bilayer.  This requires ATP created by the cell.  Active transport moves solutes against their concentration gradients, which is why it requires energy. 

Example Question #4 : Understanding Cytoplasmic Proteins

Which of the following is NOT true of the cytoplasmic protein structures known as tonofibrils?

Possible Answers:

They converge at desmosomes and hemidesmosomes.

The protein filaggrin is thought to hold them together.

They are primarily made of kertain tonofilaments.

They are primarily found in endocrine tissues.

They are most typically anchored to the cytoskeleton.

Correct answer:

They are primarily found in endocrine tissues.

Explanation:

Tonofibrils are groups of keratin tonofilaments (intermediate filaments) most commonly found in the epithelial tissues, not endocrine tissues, and which play an important structural role in cell makeup.

Example Question #1 : Understanding Second Messenger Systems

What is the primary purpose of secondary messenger systems? In other words, what can a secondary messenger do in the body that a first messenger cannot?

Possible Answers:

Secondary messengers help primary messengers cross the phospholipid bilayer by making them hydrophilic or hydrophobic.

None of these describe the unique role of secondary messengers.

Secondary messengers can take up extra space in a cell, thus limiting the ability of other chemical reactions to interfere with cell processes.

Secondary messengers are able to bind to membranes, anchoring themselves in one place, whereas primary messengers float freely throughout the cell body and are unreliable.

Secondary messengers are capable of crossing the phospholipid bilayer cell membrane, whereas primary messengers often are not.

Correct answer:

Secondary messengers are capable of crossing the phospholipid bilayer cell membrane, whereas primary messengers often are not.

Explanation:

The primary ability of secondary messengers is their ability to leave the cell membrane and travel through the phospholipid bilayer by being selectively hydrophilic or -phobic, allowing egress. This enables, for example, a cascade effect that greatly amplifies the strength of the original primary messenger signal.

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